There are known installations for removal of surplus material using the suction method as, for instance, that according to the G.F.R. Patent Specification No. 1.683.837, wherein, the surplus material being cut off, is removed by means of a suction nozzle having the form of a dome co-operating with suitable fans, and being provided with a net stretched on a frame. When the suction nozzle is brought near the surplus material being cut off the vacuum produced by the fans causes this surplus material to stick to the net, enabling it to be removed from the block of concrete, being machined. Lowering of the suction nozzle and bringing it near to the surplus material is in known machines performed by means of lifting gears.
There are also known installations of a type wherein the lowering of the suction nozzle is performed by means of a lowering mechanism driven by four lead-screws or four hydraulic cylinders, controlled by means of vacuum relays, and wherein the fans are switched on simultaneously with the actuation of said lowering mechanism. As soon as the suction nozzle approaches the surface of the surplus material, the pressure in the suction nozzle drops resulting in disengaging of the lowering mechanism by the vacuum relay at the moment when the value of pressure has reached the pre-set value. In case of considerable irregularities in the surface of the surplus material to be removed the vacuum relay responds with a certain delay, and as a result the concrete block can be damaged in case the suction nozzle is lowered too deep. Moreover, the exhaust fans running during time the suction nozzle is lowered consume large amount of the electric energy.